Sound receiver



Jan. 7, 1930. HAYES 1,743,071

S OUND RECEIVER Filed Aug. 17, 1927 avweutoz Herve C. H y $51 @MomPatented Jan. 7, 1930 PATENT OFFICE HARVEY o. Earns,

OF WASHINGTON, DISTRICT OF COLUMBIA SOUND RECEIVER Application filedAugust 17, 1927. Serial No. 213,633.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED APRIL 30, 1928; 3700. G. 757) in the use of microphones where great accuracy and uniformityof operation is required,

as in the case of binaural reception. An important feature of devices tobe used in such work is the ability to match them and this quality isnot present in the usual microphones. It is not only diflicult to matchmicrophones but they rarely remain matched for any length of time evenwhen properly matched at the outset. Various types of magneto-electricdevices commonly known as magnetophones, have been employed assubstitutes for microphones where extreme sensitivityis not required,and with the improved construction of amplifier tubes, furthermore, theneed for such great sensitivity no longer exists in the majority ofcases. I

Magnetophones heretofore employed for the reception of sound, however,have had certain inherent difiiculties which the present "nvention hassought to overcome. For example, the usual types of magnetophoneheretofore known, do not create distortionless sound receivers mainlyfor two reasons. First of all, the eddy current and hysteresis losses inthe iron commonly employed in the cores and armatures of these devices.vary with the frequency of the electrical oscillations set up.

In the second place, the variation of the reluctance of a magneticcircuit which has heretofore been commonly relied upon to produceelectrical effects corresponding to the sound or similar waves received,has a hyperbolic instead of a linear relation with respect to the motionof an armature or similar device which is moved to vary the reluctancein responseto the waves being detected. For faithful sound reception,therefore, the flux of the magnetic circuit should be kept constant andthe portions of the electrical circuits that carry the fluctuatinginduced current should have no enclosed iron. It is contemplated by thepresent invention to provide a magnetophone embracing these principlesand overcoming the inherent difficulties in the previously knowndevices. In attaining the desired results the present invention,furthermore, provides a detector which is extremely simple and one inwhich only relatively few parts, all having a constant definite relationto each other, are required. There are no loose parts or particles inthe device contemplated which mayl become displaced and remain so tovary t e effects produced.

The present improvements, furthermore, involve only extremely lightmoving parts so that their natural frequency may be made relatively highWithout requiring large forces to displace them and thereby destroyingthe sensitivity of the device. In this way, it is possible to tune thedevice to a natural frequency which is considerably above the range offrequencies to be detected. Accurate reception requires a naturalfrequency outside of the sound spectrum to be received since both theintensity and phase relation of the effects produced upon a soundreceiver change rapidly near the resonance frequency.

An incidental object produce an electric current having a relativelyhigh E. M. F. which is particularly suited for amplification. With theseand other incidental objects in view, one suitable form of embodiment ofthe invention may be 5 particularly described with reference to thedrawings in which 1 Figure 1 is a plan view of the improvedmagnetophone, and

Figure 2 is a sectional view along a diam- 9o eter line of Figure 1.

An electro-magnet, having a U-shaped core (1) formed of any suitablematerial, preferably laminated transformer steel is provided I on eachleg with a coil (2). Current from a. D. C. source 2 is passed throughthe turns of the coils in such sense as to establish op-' posite polesat the ends of the U For this purpose the coils may be connectedtogether either in series, as shown, or in parallel. Pole of theinvention is to 80 y is formed as a loop,

. conductor (6),

will be passed into pieces (3) are provided at the ends of the core andare turned toward each other so as to provide a relatively small air gapbetween them. Secured by any suitable means in a position adjacent tothe pole pieces (3) is an annular ring 4) which may be in the form of adisc having a hole at its center in line with the air gap between thepole pieces. A radial slot 5) serves to split the ring and provide anair gap or break in the circuit between the ends thus formed. If:desired, this gap may be filled by any suitable non-conductor ofelectricity. The ring or disc itself is preferably formed ofnon-magnetic material which is a good conductor of electricity. Aconductor (6), preferably made of-aluminum or copper, or other goodconductor of electricity, and relatively light in weight, the ends (7)and (8) of which are secured in any suitable way to the ring (4) atopposite sides of the slot or nonconducting portion (5). The mid-portionof the loop is bent up slightly as shown and is passed through the airgap between the pole pieces (3). A rod (9) connected to the member (6)at substantially its mid-point, is attached at its other end to somesound receiving device, such as the diaphragm; (10). A coil (11) havinga relatively large number of turns of insulated wire is mounted in agroove in the periphery of the ring or disc (4). Preferably the groovewill be lined with some insulating material such as indicated by thenumeral (12). The operation of the device is as follows:

When a sound or similar Wave strikes the diaphragm (10), the motion ofthe latter will be transmitted by the connector (9) to the which willthus be oscillated in the magnetic field between the poles (3) of theelectro-magnet. The cutting of the lines of force thus brought aboutwill serve to induce a current in the conductor (6) and this the ring(4) as by means of the contact (7), and'after traversing the ring willbe returned the contact 8) The air gap,or insulated portion (5) willinsure that the alternating current that is induced will traversesubstantially the entire circumference of the ring. Since the latter isof relatively large cross section, the current induced therein, due tothe movements of the conductor (6), will be comparatively large but ofcorrespondingly low E. M. F. The current flowing in the ring will inducea corresponding current in the coil (11) which becomes the secondary ofa transformer and due to the large number of turns in this coil the E.M. F. produced at its terminals will be relatively high while thecurrent will be comparatively small. This is the type of current whichis best suited for amplification so that the terminals of the coil mayreadily be directly connected to the input terminals"! 13) of anamplifying unit 1 through to the conductor through electrical "claimsappended. It will be noted that the construction disclosed serves toavoid the two previously mentioned difficulties inherent in similardevices previously known, thus there is no enclosed iron within thecircuit of the sound actuated armature (6) and the magnetic flux betweenthe pole pieces (3) is maintained constant throughout.

The invention herein described may be manufactured and used by or forthe Government of the United States for governmental purposes withoutthe payment tome of any royalty thereon or therefor.

What I claimis:

1. In a sound detector an electro-magnet having a relatively small airgap provided between the poles thereof, an annular member of goodelectrical conductivity, said member having a radial slot therein, anarmature having its ends connected to said member adj acent oppositesides of said slot the mid-portion of said armature being oscillatablein the air gap between said poles, means for oscillating said armaturein accordance with the sound waves to be detected, and a coil "mountedon said member adapted tohave a current induced therein in accordancewith the movements of said armature.

2. In a vibration detector an electro-magnet having its poles soarranged as to form a small air gap, an electrical conductor passingsaid air gap substantially mid-way between said poles, a secondrelatively large electrical conductor connected at opposite ends to saidfirst conductor, a coil mounted on said second conductor, and means forvibrating said first mentioned conductor in accordance with thevibration to be detected whereby a current will be induced in said coil.

3. A device for generating electrical impulses comprising a magnet,' asplit ring, an

conductor having its ends connected to said ring and having anintermediate portion passing through the field of said magnet, a coilmounted on saidring, said coil having its turns concentric with saidring, and means for vibrating said intermediate portion of saidconductor thereby inducing a current in said coil.

4. A device for generating electrical im pulses of relatively highpotential compris ing a split ring, a coil mounted on said ring,

I so

' said coil having its turns concentric with respect to said ring, andmeans for inducing a current of low potential in said ring whereby arelatively high potential is created in said 5. A vibration detectorcomprising a magnet, a split ring of good electrical conductivityadjacent said magnet, a coil mounted on said ring, an electricalconductor connected to said ring, and means responsive to the vibrationto be detected'for moving a portion of said conductor across the fieldof said magnet.

6. A vibration detector comprising an electro-magnet having its poles inclose prox imity, a disc of good electrical conductivity arrangedadjacent said magnet poles, said disc having an openin at its center anda radial slot extending rom said opening to the periphery of said disc,a coil mounted in the periphery of said disc, a conductor having itsends attached to said disc at opposite sides of said slot, and meanspassing through the opening in said disc adapted to vibrate a portion ofsaid conductor in the field of said magnet in response to the vibrationsbeing detected.

7 In a device of the class described, a magnet, a ring of non-magneticmaterial adjacent the poles of said magnet, means connected to said ringand movable across the field of said magnet to induce a current in saidring, and a coil in inductive relation with respect to said ring.

8. In a device of the class described, an electro-magnet, a disc ofnon-magnetic material mounted in contact with the poles of said magnet,said disc having a radial slot and a central aperture formed therein, alight electrical conductor having its ends secured to said disc atopposite sides of said slot, means for moving a portion of saidconductor across the field between the poles of said magnet and a coilin inductive relation with respect to said disc.

9. In a device of the class described, a magnet, a coil mounted adjacentsaid magnet, and an electrical conductor mova'ble in the field of saidmagnet and adapted upon movement to induce currents in said coil, saidcoil being so mounted as not to enclose any magnetic material.

10. In a device of the class described, a magnet adapted to establish aconstant flux, a coil mounted adjacent said magnet, and an electricalconductor movable in the field of said magnet and adapted upon movementto set up induced currents in said coil, said conductor being soarranged as not to completely surround any magnetic material.

HARVEY C. HAYES.

